1. Field of Invention
The invention pertains to the field of visual perception, specifically to an arrangement for inducing certain novel and useful perceptions. These perceptions can create special visual effects for films, television, and other forms of entertainment. Also they can be used to evaluate visual dysfunction.
2. Background--Prior Art--FIGS. 1A-1C
It is known that when a human's two eyes see different images, it is possible to arrange the images so as to create a "competition" between the two eyes which can produce novel perceptual effects. In other words, if the two eyes send respective signals representing a pair of images to the visual centers of the brain, the visual centers will try to combine components parts of the two signals into a single perception. However, when the information contained by the images is incompatable, the visual center may selectively inhibit some of the information in forming the perception. This may be described as a "rivalry" between the eyes, though it should be understood that any synthesis or transformation of the information coming from each eye is accomplished by the brain.
FIG. 1A shows a prior-art visual set of images (called "stimuli" by Psychologists), comprising a black line drawing 11 of a multifaceted polygon with a white background surface, and a white line drawing 12 of the same polygon with a black background. These stimuli are paired to form stereoslide 10, which can be viewed stereoscopically to produce the perception of a single image which has a lustrous "gun-metal" surface. This is because the dark and light regions of the stimulus cause competition between the eyes (called binocular rivalry). This example of binocular rivalry was provided by H. von Helmholtz (Handbuch der Physiologischen Optik, 1910, plate IV-Q).
FIG. 1B shows a prior art stereoscopic slide 20 used by W. J. M. Levelt ("Binocular brightness averaging and contour information," British Journal of Psychology, 1965, pp. 1-13). This slide provides the right eye with a view of three black disks (22, 24, 26), while the left eye sees a hollow disk 21, a black disk 23, and a blank area 25 at the corresponding locations of the binocular visual field. When slide 20 is examined through a stereoscope, ring 21 is combined with disk 22, disk 23 is combined with disk 24, and blank area 25 is combined with disk 26. The perception which results is shown in Fig 1C; the viewer will perceive a bright disk at 31 and dark disks at 32 and 33. Using this stimulus configuration and these viewing requirements, Levelt was able to induce an increase in brightness in the immediate neighborhood of the stimulus contours, with the strength of the effect depending upon the size of the stimulus.
Observations by Helmholtz (op. cit.) and by those who preceded him had established that binocular conflict could produce the perception of luster, either when the images were presented by stereoscope or by viewing the objects through colored filters. However, none were accurate in establishing the essential conditions for producing the effect. H. W. Dove (Poggendorffs Ann. LXXXIII, 1850, p. 169) thought that differential refraction by the two eyes created depth cues which caused the images to be seen in different planes. This does not explain why the luster can be seen with black-and-white or monochromatic images. Helmholtz (op. cit., pp. 417-418) thought the luster was produced by a differential level of stimulation (i.e. a difference in brightness) at correponding points on the two eyes. When an observer with normal binocular vision fixates upon a real object, it provides the same brightness level to the corresponding point in each of the eyes. Under the unusual viewing conditions provided by the stereoscope, however, it is possible to provide the corresponding locations with different brightness levels, and Helmholtz thought this was the key factor in producing the perception of luster. As detailed below, the differential level of brightness is a factor in producing luster, but it is not the only factor. If it were, the binocular synthesis of disk 26 with blank area 25 would produce the perception of luster, since there is a brightness differential at corresponding locations of the two retina. In fact, this combination produces the perception of disk 33, which is seen as dark and having no luster. Levelt (op. cit.) described means by which contours would produce local control of brightness. His means included the centering of the stimulus within the field of view, because his analysis found that the local effects were strongest at the fovea. He stated that the strength of the brightness control was determined by the size of the stimulus, and his means for producing local control included the superimposition of the edges of the stimulus object presented to each eye.